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CVE-2026-100390 – IP-Based Access Control Bypass via IPv6 Spoofing – Zoraxy 3.2.3–3.3.4

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Summary

CVE-2026-100390 is an authentication bypass vulnerability (CWE-290, Authentication Bypass by Spoofing) affecting the Zoraxy reverse proxy. Zoraxy versions 3.2.3 through 3.3.4 fail to properly parse IPv6 addresses in the RemoteAddr field when setting forwarded headers, allowing an unauthenticated network attacker to spoof their source IP and bypass IP-based access controls enforced by Zoraxy’s authorization provider. The flaw carries a CVSS v4.0 base score of 9.1 (Critical).

Technical details

  • Root cause: Zoraxy’s forward-auth logic (util.go) does not correctly parse IPv6 addresses supplied in the RemoteAddr field before using them to construct forwarded headers such as X-Forwarded-For.
  • Trigger condition: An attacker connects to a Zoraxy-fronted service over IPv6 and supplies a crafted RemoteAddr/forwarded-header value that the parser mishandles.
  • Attack vector: Network-based, unauthenticated, no user interaction required.
  • Impact: The malformed parsing lets an attacker inject an arbitrary X-Forwarded-For value, effectively spoofing their client IP. Any downstream authorization provider or access-control rule relying on the forwarded client IP can be bypassed, allowing unauthorized access to resources that were meant to be restricted to trusted IP ranges.

Affected software

  • Zoraxy versions 3.2.3 through 3.3.4 (inclusive)

Severity

  • CVSS v3.1 Base Score: 7.4 (High) — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
  • CVSS v4.0 Base Score: 9.1 (Critical) — CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade Zoraxy to version 3.2.5 or later, where the IPv6 RemoteAddr parsing logic has been corrected and stricter validation is enforced on forwarded headers.
  • If no patch can be applied immediately:
    • Do not rely solely on IP-based access control for sensitive resources behind Zoraxy; require additional authentication factors such as MFA or client-certificate verification.
    • Strip or validate X-Forwarded-For and related forwarded headers at the network perimeter (firewall or WAF) before traffic reaches Zoraxy.
    • Where feasible, restrict or disable IPv6 connectivity to Zoraxy-fronted services until patched.

References

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